Dressed head to toe in white, Michael Fossum and Ronald Garan Jr. looked like puffy dolls against the 37-foot-long, 14-foot-wide lab, which is now the biggest room at the International Space Station.

It was their second spacewalk in three days at the shuttle-station complex, orbiting 210 miles above Earth.

“I feel like I’m on a camping trip trying to pack up a wet tent on a Sunday morning,” Fossum said as he wrestled with some of the lab’s insulation. He and Garan removed thermal covers from the lab’s robot arm and added them to a variety of attachment points.

As the spacewalkers toiled outside, their eight colleagues hauled more experiment racks into the billion-dollar lab, called Kibo, Japanese for hope, and flight controllers near Tokyo monitored the power systems.